Polymers find uses in a variety of plastic articles including films, sheets, fibers, foams, molded articles, adhesives and many other specialty products. The majority of these plastic materials ends up in the solid waste stream. While some efforts at recycling have been made, repeated processing of even pure polymers results in degradation of material and consequently poor mechanical properties. Different grades of chemically similar plastics mixed upon collection can cause processing problems that make the reclaimed material inferior or unusable. Thus, there is a need for plastic articles which are biodegradable.
Used solid articles may occupy a large volume, and may be inconvenient when used in an environment of limited waste disposal options, such as an ocean-going ship which would have to contain its solid refuse until reaching shore. Further, solid articles may become hazardous or controlled waste requiring special treatment, such as the autoclaving of hospital or other medical waste. Thus, there is a need for a method of converting solid articles to a liquid form, preferably a biodegradable liquid form. Preferably, the conversion could occur simultaneously with a decontamination step, such as during steam autoclaving of hospital and medical waste.
Honeycutt, U.S. Pat. Nos. 5,181,967, 5,207,837 and 5,268,222, and Honeycutt et al., U.S. Pat. No. 5,470,653, disclose articles made of polymers which are water soluble at high temperatures, such as propylcellulose, polyvinyl alcohol, and copolymers of polyvinyl acetate and polyvinyl alcohol.
Patnode et al., U.S. Pat. Nos. 5,472,518, 5,508,101, 5,567,510 and 5,630,972, disclose aqueous-alkaline disposable articles comprising a hydrolytically degradable polymer such as polymers and copolymers of poly(lactic acid), poly(ester amide), poly(glycolic acid), poly(vinyl alcohol), poly(hydroxybutyrate-co-valerate). Patnode et al. teach that the articles will disperse during a single commercial laundry cycle into waste water having a basic pH less than 12 and an elevated temperature.
Japanese Patent Application No. 08-253,619 discloses a method of disposing of molded plastic products containing biodegradable resin having an ester bond by contacting the molded product with a solution containing at least an alkali metal compound or an alkaline-earth metal compound, and an alcoholic compound. Among the ester bond-containing biodegradable resins which are disclosed are polyhydroxyvaleric acid, polyhydroxybutyric acid, hydroxyvaleric acid copolymers, polycaprolactone, polyhydroxylbutyric acid, polyethylene succinate, polyethylene glutarate, polyethylene adipate, polybutylene adipate, polybutylene succinate, and polybutyric acid.
Ajioka et al., U.S. Pat. No. 5,780,704, discloses a process for decomposing a thermoplastic polymer composition comprising a polyhydroxycarboxylic acid base polymer by contacting the polymer with an alkaline solution of a pH of 10 or more to produce hydroxycarboxylic acid. Ajioka et al. further disclose that suitable polyhydroxycarboxylic acid base polymers include polymers of lactic acid, glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, and 6-hydroxycaproic acid.
Satoh et al., Polymer, Vol. 35 (2), pp. 286-290 (1994), teach that the addition of poly(hydroxybutyrate-co-hydroxyvalerate) to a film of poly(hydroxybutyrate) could decrease the level of crystallinity in the blend, and the lower the initial crystallinity of the films, the higher the rate of hydrolytic degradation.
Holmes, U.S. Pat. No. 4,620,999, and EP 0 142 950 A, teaches disposable bags for body-waste comprising a 3-hydroxybutyrate polymer and a basic material to modify the pH of the bag contents to a pH of at least about 12. Holmes teaches that modifying the pH of the contents increases the rate of the polymer's degradation.
Noda, U.S. Pat. No. 5,918,747, discloses a process for recovering polyhydroxyalkanoates from biological sources. Noda further teaches the polyhydroxyalkanoates can be used to form disposable health care products such as bandages, wound dressings, wound cleansing pads, surgical gowns, surgical covers, surgical pads and bedding items such as sheets, pillowcases and foam mattress pads.
Unfortunately, many prior art plastic items comprise plasticizers, are lacking in strength or have poor water permeation resistance and/or grease permeation resistance. Further, many biodegradable items are brittle, are incapable of degrading under both aerobic and anaerobic conditions, or can not be easily digested to a non-viscous biodegradable liquid.
Additionally, prior art polymers such as polyhydroxybutyrate and polyhydroxy-butyrate-co-hydroxyvalerate often have unsatisfactory properties. Polyhydroxybutyrate tends to be thermally unstable, while polyhydroxybutyrate and polyhydroxybutyrate-co-hydroxyvalerate often have slow crystallization rates and flow properties which make processing difficult. For example, polyhydroxybutyrate-co-hydroxyvalerate remains tacky for long periods of time, and may stick to itself when being processed into films.
Other polymers, like polylacticacid and polyhydroxyoctanoate, become excessively soft at even moderate temperatures below 80° C. This limits their utility in many applications.
Many polymers which may be dissolved in hot water, such as poly(vinyl alcohol) polymers, will form highly viscous and sticky solutions which are difficult to handle and dispose. Other polymers, such as polycaprolactone or succinic acid copolymers, digest slowly or to a limited degree when treated with alkaline solutions. Other polymers undergo alkaline digestion at a convenient rate only at extremely high temperatures, such as greater than about 170° C. Such high temperatures may not be reached by some simple steam systems, such as steam autoclaves. Thus, there is a need for a polymer which can form ductile and flexible articles, and which can be quickly and conveniently digested to form a non-viscous liquid wherein the liquid itself is biodegradable.